Gas hydrates are solids that may form during hydrocarbon production, in particular in pipelines and other equipment, that may impede or completely block flow of hydrocarbons. These blockages not only decrease or stop production, potentially costing millions of dollars in lost production, but are also very difficult and dangerous to mediate. Unless properly handled, gas hydrates may explode, rupturing pipelines, damaging equipment, endangering workers and putting at risk the ocean environment.
Gas hydrates may form when water molecules become bonded together after coming into contact with certain “guest” gas molecules. Hydrogen bonding causes the water molecules to form a regular lattice structure that is stabilized by the guest gas molecules. The resulting crystalline structure precipitates as a solid gas hydrate. Guest molecules can include any number of molecules, including carbon dioxide, methane, butane, propane, hydrogen, helium, freons, halogens, and noble gases.
Various types of inhibitors may be used to control formation or the effect of gas hydrates. One example is anti-agglomerate gas inhibitors, which are typically more cost effective than certain other inhibitors, as anti-agglomerate gas inhibitors may be used in much lower concentrations and are typically useful in environments with greater subcooling than would be appropriate for other inhibitors. However, many of the traditional anti-agglomerate LDHI's contain residual halides, such as HCl, HBr, and the like, and residual organic halides. Residual halides have been known to cause corrosion and stress corrosion cracking (“SCC”) in metal piping and production equipment. One example of a commonly used anti-agglomerate LDHI is a quaternary anti-agglomerate containing residual organic halides, such as Kelland, 2006. As an example, Milburn et al. U.S. Pat. No. 6,444,852 entitled “Amines Useful in Inhibiting Gas Hydrate Formation,” which is hereby incorporated by reference in its entirety, describes anti-agglomerate ether-containing amine compounds that are quaternized with a halide (“quaternary amines”).
It is has been determined that LDHIs have contributed to and/or responsible for general corrosion and, in particular, pitting corrosion in certain subsea applications. This corrosion seems particularly acute in deep sea applications. It is believed residual halides present in LDHIs, in particular quaternary amine-containing LDHIs are responsible for these types of corrosion. While traditional acid corrosion inhibitors have been utilized in an effort to control this corrosion, the traditional acid corrosion inhibitors have not been particularly effective.
What is needed is a method of controlling the general corrosion and pitting corrosion in metals in undersea oil and gas production applications that are exposed to halide containing LDHIs, in particular, quaternary amines.